1. Field of the Invention
The present invention relates to a camera system comprising: a camera head having an image taking optical system and an imaging device; and a camera main frame on which the camera head is detachably mounted, the camera main frame applying signal processing to an image signal received from the camera head.
2. Description of the Related Art
Hitherto, there is proposed a camera system wherein when a plug-in unit, in which an imaging device is integral with an image taking optical system, is mounted on a camera main frame, information of the plug-in unit is transmitted to the camera main frame, so that the image taking optical system of the plug-in unit can perform photography (Japanese Patent Application Laid Open Gazette TokuKai Hei. 8-172561). Implementation of the camera system, in which an interchange of the image taking optical system or an image taking lens is carried out in such a way that the plug-in unit is simply mounted on the camera main frame, makes it possible that treatment of the camera system is very simplified, and whereby a person, who has no expert knowledge, can perform an interchange of the image taking lens.
As the similar camera system, there is proposed a camera system comprising: a camera head having an image taking optical system and an imaging device; and a camera main frame on which the camera head is detachably mounted, the camera main frame applying signal processing to image signal received from the camera head (Japanese Patent Application Laid Open Gazette TokuKai 2000-175089).
By the way, in the camera system having the camera head and the camera main frame, there is frequent such a case that the camera main frame is provided with a release button and the camera head is provided with an imaging device. In this case, when the release button of the camera main frame is subjected to a full-depression operation, a release signal according to the full-depression operation of the release button is transmitted via an interface placed between the camera head and the camera main frame to the imaging device of the camera head, so that the exposure of the imaging device is started. As the interface as mentioned above, there is used, for example, a serial interface (SIF) for a bilateral direction communication so that information necessary for imaging can be exchanged between the camera head and the camera main frame. In case of such an interface, in order to reduce the number of parts, there is provided such an arrangement that all control signals including the release signal that is one of the signals necessary for the imaging operation are supplied via the interface from the camera head to the camera main frame or from the camera main frame to the camera head.
However, in the event that the interface is occupied when it is intended that the release signal is supplied from the camera main frame via the interface to the imaging device of the camera head at the timing of the full-depression of the release button, the release signal is supplied after the occupation of the interface is terminated. For this reason, there will occur a time lag between a timing of the depression of the release button and an exposure start timing that ought to be the substantially same as the timing of the depression of the release button. The larger time lag, the later the exposure start time on the imaging device as compared with the release operation time. As a result, it is difficult to catch the subject at the intended release operation timing and it is obliged that the subject is caught in timing later a little. In the event that the still subject is photographed, it is not so effective, but in the event that the active subject is photographed, the occurrence of the time lag may oblige an operator to take a picture of a subject after a subject to be caught at the shutter chance is moved.
When the release button of the camera main frame is depressed, the release signal is transmitted via the interface between the camera head and the camera main frame to the imaging device of the camera head. A photometry section of the camera head performs photometry in accordance with the release signal. In some photometric value, it needs a flash light emission, and thus a light emission instruction signal for instructing the flash light emission is transmitted from the camera head via the interface to the camera main frame and the flash light is emitted, so that an exposure of the imaging device of the camera head is started.
However, in the event that the photometry section of the camera head performs photometry in timing of depression of the release button and it needs the flash light emission, if the interface is occupied, then there will occur a time lag between a timing that the light emission instruction signal is supplied to a flash light emission section and a timing of the release button operation. Thus, when the time lag occurs between the timing of the release button operation and the timing of supplying the light emission instruction signal, the time lag would prevent the proper light quantity to be supplied to a photo-receiving surface of the imaging device by the flash light emission from being supplied to the photo-receiving surface of the imaging device.
The influence by the time lag more extremely appears, as the shutter speed is higher. As an example that the influence by the time lag extremely appears, there is raised a daytime synchro-flash photography. What is meant by the daytime synchro-flash photography is that in the daytime a part of the subject intended in photography is involved in shadow, and a projection of the flash light to the shadow portion serves to remove the shadow so that the clear photography can be expected.
According to such a daytime synchro-flash photography, in view of the daytime, the photography is performed with the shorter of the shutter speed, and thus if the time lag occurs, it may happen that the flash light is emitted after the completion of the exposure.